Electronic endoscope systems adopt either a field-sequential technique or a simultaneous technique. According to the field-sequential technique, red (R), green (G), and blue (B) illumination light rays are irradiated to an object. The red, green, and blue illumination light rays reflected from the object are converged on a solid-state imaging device, red, green, and blue video signals produced by the solid-state imaging device are synthesized to produce a color video signal. According to the simultaneous technique, white light reflected from an object is split into red, green, and blue object light rays using a color filter. Solid-state imaging devices associated with red, green, and blue produce video signals from the red, green, and blue object light rays, and the object video signals are synthesized to produce a color video signal.
Many endoscopes adopt the field-sequential technique because an insertion member to be inserted into a body cavity must be thin and a produced video signal must offer a high resolution.
An electronic endoscope system adopting the field-sequential technique is disclosed in, for example, Japanese Patent No. 306123. Illumination light irradiated from a light source lamp is propagated to a light guide by way of a rotary filter and a condenser lens. The illumination light guided by the light guide is irradiated to an object, and light reflected from the object is converged on a solid-state imaging device.
The rotary filter is driven to rotate at a predetermined rps using a motor. Light is passed through red, green, and blue transmission filters that cover three fan-shaped openings formed on the perimeter of the rotary filter. Consequently, red, green, and blue illumination light rays are irradiated to an object.
The red, green, and blue light rays produced by the rotary filter and reflected from the object are converged on the solid-state imaging device. Red, green, and blue video signals produced by the solid-state imaging device are synthesized to produce a color video signal.
A photosensor is provided on the rotary filter at the perimeter thereof to detect an open period of the openings. The photosensor detects a pulse signal that indicates the open period of the openings. Using the pulse signal, a pulse current for lighting the light source lamp is produced.
In other words, during the open period of the openings covered with the red, green, and blue transmission filters included in the rotary filter is unblocked, the pulse current is superposed on a predetermined constant current which lights the light source lamp. The resultant current is then supplied to the light source lamp.
When the light source lamp is lit using the pulse current, a white balance can be readily adjusted within a light source device by controlling the duty cycle or value of the pulse current.
In a conventional electronic endoscope, illumination light irradiated from a light source lamp is converted into red, green, and blue illumination light rays using red, green, and blue transmission filters included in a rotary filter. The red, green, and blue illumination light rays are propagated over a light guide, and successively irradiated to an object. Red, green, and blue object light rays reflected from the object are converged on a solid-state imaging device, and photoelectrically converted into red, green, and blue object video signals.
The red, green, and blue object video signals are synthesized to produce a television video signal. When the television video signal is produced by synthesizing the object video signals, white balance adjustment is needed in order to synthesize the red, green, and blue object video signals at a predetermined ratio.
The white balance adjustment falls into a method for adjusting a lighting current for lighting a light source lamp with each red, green, and blue transmission filter provided at the openings of the rotary filter, and a method for electrically synthesizing the red, green, and blue object video signals produced by the solid-state imaging device.
Aside from the white balance adjustment, driving of a diaphragm that optimizes an amount of illumination light which is emitted from the light source lamp and irradiated to an object by way of the rotary filter and light guide must be controlled.
The regulation of a lighting current for lighting the light source lamp and control of driving of the diaphragm that adjusts an amount of light irradiated to an object, which are required for the white balance adjustment, are achieved by a skilled worker, who uses a predetermined adjustment jig, in the course of manufacturing the electronic endoscope system. Moreover, when the light source lamp included in the electronic endoscope system is replaced with a new one because of termination of the service life thereof, or when the light source lamp is repaired, the white balance adjustment and the adjustment of the diaphragm for regulation of the brightness level of a view image must be performed again using the adjustment jig.
As mentioned above, especially when the light source lamp is replaced with a new one or repaired, the white balance adjustment and the adjustment of the brightness level of a view image must be performed again. At this time, the adjustment jig is needed as a repairing instrument. Moreover, a worker skilled in the white balance adjustment or the adjustment of the brightness in a view image must perform the adjustment by taking much time.
Accordingly, an object of the present invention is to provide an adjusting method for endoscope systems that permits quick and reliable white balance adjustment and light level adjustment for illumination light without the necessity of an adjustment jig.